1. Field of the Invention
The present invention relates generally to refrigeration systems and, more particularly, is concerned with a refrigeration system which uses a liquid refrigerant which remains in the liquid phase throughout the system and which liquid refrigerant is cooled by liquid nitrogen.
2. Description of the Prior Art
Refrigeration systems have been described in the prior art. However, none of the prior art devices disclose the unique features of the present invention.
In U.S. Pat. No. 5,293,759, dated Mar. 15, 1994, Lee, et al., disclosed an absorption refrigeration system which uses a solution and a refrigerant contained in the solution as working mediums. The system includes (a) a generator for heating the solution to change a portion of the refrigerant into vapor; (b) a condenser communicated with the generator, for condensing refrigerant vapor coming from the generator; (c) a throttling device communicated with the condenser, for throttling condensed refrigerant coming from the condenser; (d) an evaporator communicated with said throttling device, having water circulating therewithin, capable of effecting heat transfer between the refrigerant coming from the throttling device and the circulating water; (e) an absorber communicated with the evaporator, having solution reservoired therewithin, for absorbing refrigerant coming from the evaporator by means of the reservoired solution; and (f) a heat exchanger communicated with the absorber and the generator, for performing indirect heat exchange between solution coming from the generator and solution coming from the absorber, characterized in that a solution mixing device, disposed between the heat exchanger and the generator, is provided for mixing solution leaving the generator and solution going to enter the generator. The system disclosed is capable of increasing the performance of heat transfer in the generator and reducing the cost of the generator, and thermal stress will also be reduced.
In U.S. Pat. No. 5,018,359, dated May 28, 1991, Horikawa, et al., disclosed a cryogenic refrigeration apparatus which includes a thermal shield, a vacuum vessel and a magnetic shield which are telescopically arranged in that order toward the exterior of a cryogenic vessel which accommodates a superconducting coil, a refrigerator for cooling the thermal shield is securely supported on the thick-walled magnetic shield. Accordingly, vibration produced by the refrigerator is suppressed by the magnetic shield, whereby noise is suppressed which is produced in the vacuum vessel to the magnetic shield through a bellows.
In U.S. Pat. No. 5,586,437, dated Dec. 24, 1996, Blecher, et al., disclosed an MRI cryostat which contains a superconducting magnet operating in a bath of liquid helium, reduces the boil-off rate of helium by intercepting most of the heat in-leakage by means of a throttle cycle (TC) refrigerator operating at a low side temperature of about 90K. The main heat exchanger for the throttle cycle refrigerator is located within or immediately adjacent to the cryostat housing and delivers cold liquid to a cold heat exchanger that is in thermal contact with an outer radiation shield, support struts, nock tube and electrical leads inside the cryostat. Heat is intercepted by the outer shield from essentially all paths between a 300K ambient and a 4K load temperature, which temperature results from liquid helium boil off to atmosphere. A second, inner radiation shield at 35K is cooled by gaseous helium that boils from the liquid helium bath. There are no moving parts of the refrigeration system in the cryostat. Thus, vibration, noise and disturbance of the magnetic field are reduced. The refrigerator installation is small and low in cost; power consumption is reduced relative to the prior art.
In U.S. Pat. No. 5,314,007, dated May 24, 1994, Christenson disclosed the combination of a converter in which liquid petroleum gas is changed in phase from liquid to gas preparatory to fueling an internal combustion engine by adding heat from a fluid, a dual three-way valve, as air-fluid heat exchanger is a human-occupied compartment (the cab), and a fluid circulation system independent of the internal combustion engine cooling system. The dual three-way valve""s position either directs engine coolant tapped from the engine through the converter and air-fluid heat exchanger, partially cooling the cab, or directs fluid from the independent fluid circulation system through the converter and air-fluid heat exchanger, fully cooling the cab. As an alternate embodiment for installations when engine coolant can become temporarily too hot to exit the inverter below ambient cab temperature, an independent bypass may be incorporated.
In U.S. Pat. No. 5,560,212, dated Oct. 1, 1996, Hansen disclosed an air conditioning system for cooling a cabin of a vehicle. The vehicle has combustion chambers and a cooling system which circulates vehicle coolant. The cooling system also includes a radiator and an intake manifold. The air conditioning system includes a source of a liquid gas which is connected to the combustion chambers with a first heat exchanger positioned between the source and the combustion chambers. A coolant line also extends through the first heat exchanger whereby a coolant passing therethrough is cooled via vaporization of the liquid fuel. A pump is connected to the coolant line and circulates the coolant through the air conditioning system. The coolant line is also connected to a second heat exchanger whereby coolant passing through the second heat exchanger is heated and thereby cools the air. The now heated coolant circulates back to the first heat exchanger.
In U.S. Pat. No. 5,490,398, dated Feb. 13, 1996, Cline disclosed an absorption heating and cooling system in which an absorbent/refrigerant fluid is circulated in a fluid flow loop having a condenser, a metering device, an evaporator, an absorber and a generator chamber. A magnetron provides a heat source for the generator chamber which also contains electrodes to facilitate vaporization of the refrigerant. The vaporized refrigerant and entrained moisture passes from the generator chamber to an electromagnetic vapor scrubber to further ionize the fluid. The ionized fluid passes through a metering device which reduces the pressure and temperature of the fluid. The refrigerant then passes to an evaporator where it contacts a heat exchange medium which transfers heat to the refrigerant in order to achieve a desired cooling effect. The refrigerant then passes from the evaporator to the absorber and back to the generator chamber to repeat the cycle.
The present invention discloses a self-contained recirculating refrigeration system wherein the refrigerant is referred to as HTF (heat transfer fluid) which is cooled using liquid nitrogen. HTF remains in the liquid phase throughout the process of the present invention. The basic process can be viewed as beginning with the injection of liquid nitrogen (LN2) from a liquid nitrogen supply tank into the thermal converter wherein the heat transfer fluid (HTF) is cooled by LN2 through one or more heat exchangers to let the LN2 absorb heat from the HTF and thereby cool the HTF to refrigeration temperatures. The rate at which LN2 enters the thermal convector is controlled by a valve so as to maintain the temperature of the HTF at a set point. This process causes the liquid nitrogen to change phase and to be converted into a gaseous nitrogen state (GN2) which GN2 is then transferred through a conduit into the pre-cooler tank to allow for a pre-cooling of the HTF prior to HTF entering into the pump system. Used GN2 is discharged to the atmosphere from the pre-cooler tank. HTF from the thermal converter is conveyed through a conduit to the various freezers, refrigerators, air conditioning systems or the like, or any other process equipment requiring cooling. The HTF conduit can be connected to an existing refrigeration system without modifying the existing refrigeration piping by using a manifold. The return line carries HTF from the refrigeration device back to the neutral tank. The neutral tank feeds into the top pipe that is located on the pre-cooler tank and then discharges HTF out after the HTF is pre-cooled by GN2 to the pump whereby the pumping system will inject used HTF into the thermal converter at which point the process is repeated.
An object of the present invention is to provide a refrigeration system which eliminates moving parts associated with the conventional refrigeration system. A further object of the present invention is to provide an inexpensive refrigeration system to operate. A further object of the present invention is to reduce the capital cost of the refrigeration system.
Advantages of the present invention are that it eliminates the need for a compressor, condenser and various associated hardware of a conventional refrigeration system. Since the compressor is the most costly component of a traditional refrigeration system to purchase, maintain and operate, the present invention has a primary goal of reducing energy cost by approximately 35% or more. The savings in cost of operations of the present invention increases in relation to the facility size. The system has few moving parts so maintenance costs are reduced. Additionally, it is the determination of the USEPA and World-Wide Environmental Agencies to eliminate Freon usage in commercial and industrial refrigeration by the year 2008. The present invention contains no HCFC""s, CFC""s, Freon or Ammonia products. Liquid nitrogen from which the system derives its cooling BTU content is about 78% of the earth""s atmosphere and is inexpensive in bulk quantities and environmentally compliant.
Additional objects and advantages of the present invention will appear as the description proceeds.
The foregoing and other objects and advantages will appear from the description to follow. In the description reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments will be described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the scope of the invention. In the accompanying drawings, like reference characters designate the same or similar parts throughout the several views.
The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is best defined by the appended claims.